Field of the Invention
The invention relates to a method of operating a sheet-processing machine, having a sheet-pile station, a sheet conveyor for feeding the sheets to the pile station and for releasing them thereat during operation, the sheet conveyor defining an upper limit of a space extending beneath the sheet conveyor in the pile station and having a magnitude depending upon the operating condition of the machine, and a drive operatively connected to the sheet conveyor.
In sheet-processing printing machines such as are sold, for example, by the Heidelberger Druckmaschinen A.G., a German corporation of Heidelberg, Germany under the model designation SM102, the processed sheets form, in a sheet-pile station, sheet piles which are deposited on a lifting platform, vertically adjustable by a lifting mechanism and, in one of the possible pile-formation operating modes, rest in each case on a pile base, generally in the form of a pallet, that has been deposited on the lifting platform. Before the start of a respective print job, the lifting platform is adjusted by the lifting mechanism to such a raised position that the upper side of the yet empty pile base is located at a production level. A sheet conveyor receives the processed sheets from a last processing station of the printing machine, guides them to a level located a drop distance above the production level, over the pile base adjusted to the production level, and releases them for braking by a sheet-braking system and for subsequent pile formation. In the course of the pile formation, the lifting mechanism lowers the lifting platform automatically in a stepwise manner to the same extent as the height of the pile increases, with the result that the sheets sequentially following one another in production printing cover an essentially constant drop distance between the sheet conveyor and the production level, which is essentially maintained by the stepwise lowering of the lifting platform.
In addition to the automatic lowering of the lifting platform, a motor which actuates the lifting mechanism can also be activated manually to raise and lower the lifting platform. In particular, it is also possible for the lifting platform to be lowered completely without having a sheet pile set down thereon, thereby producing, between the lifting platform and the sheet conveyor, a clearance space that is of such a magnitude that, in particular, an operator can gain access thereto. Only when the sheet conveyor is at a standstill is this not problematic, and is even desirable inasmuch as it allows access to the clearance space in order to perform, for example, adjustments to the sheet-braking system so that braking rollers or braking belts forming the system are adapted manually to the format of the processed sheets and are adjustable, if necessary or desirable, to print-free areas of sheets printed on both sides, or in order for sheet supports provided, for example, in the form of so-called tail or nosewheels to be positioned as the conditions require.
Before a subsequent startup of the printing machine and, in particular, the sheet conveyor, an acoustic warning signal is then given in conventional printing machines in order to alert the operator working in the clearance space to leave the space and thus avert any risks posed by the sheet conveyor, which then revolves above the clearance space.
This operator-protection measure, however, also requires the operator to be vigilant and, in particular, to comply with the request, which in this case goes hand-in-hand with the latter to leave the clearance space.
It is accordingly an object of the invention is to provide a method of operating a sheet-processing machine wherein the safety risk for operators working in the region of a delivery thereof during the operation is reduced.
With the foregoing and other objects in view, there is provided, in accordance with one aspect of the invention, a method of operating a sheet-processing machine having a sheet-pile station, a sheet conveyor for feeding sheets to the sheet-pile station and for releasing the sheets thereat during operation, the sheet conveyor defining therebeneath a clearance space extending downwardly with a magnitude depending upon the operating state of the machine, and a drive operatively connected to the sheet conveyor, which comprises detecting extents of the clearance space in a vertical direction which exceed predeterminable values, and, after the drive has been stopped, forcibly keeping the drive stopped for as long as the vertical extent of the clearance exceeds a predetermined value.
In accordance with another mode, the method invention comprises forcibly stopping the drive after a prior startup thereof, if the extent of the clearance space exceeds a predetermined value.
In accordance with a further mode, the method invention comprises, after a prior startup of the drive, for an extent of the clearance space beyond a predetermined value, forcibly feeding to the sheet-pile station only those sheets which were on the way for sheet processing, and then forcibly stopping the drive.
In accordance with an added mode, the method invention comprises, during the feeding of those sheets to the sheet-pile station, which were on the way to sheet processing, preventing the extent of the clearance space from being increased in size.
In accordance with an additional mode, the method invention comprises introducing into the clearance space a divider that is bringable into and removable out of the clearance space, the extent of the clearance space being limited to a predetermined value.
In accordance with a concomitant aspect of the invention, there is provided a method of operating a sheet-processing machine having a sheet-pile station, a sheet conveyor for feeding sheets to the sheet-pile station and for releasing the sheets thereat during operation, the sheet conveyor defining therebeneath a clearance space extending downwardly with a magnitude depending upon the operating state of the machine, and a drive operatively connected to the sheet conveyor, which comprises detecting extents of the clearance space in a vertical direction, which exceed predeterminable values, and forcibly reducing to a predetermined value an extent of the clearance that exceeds a predetermined value.
Thus, in order to achieve the object of the invention, a sheet-processing machine, in particular a printing machine, having a pile station, a sheet conveyor by which the sheets can be fed to the pile station, a clearance space extending beneath the sheet conveyor and being of a magnitude which depends upon the operating condition of the machine, and a drive that is operatively connected to the sheet conveyor, is operated, in one operating mode, so that vertical extents of the clearance space which exceed predeterminable values are detected and, after stoppage of the drive, the latter is forcibly kept stopped for as long as the vertical extent of the clearance exceeds a predetermined value, while, in another operating mode, vertical extents of the clearance space which likewise exceed predeterminable values are detected, and an extent of the clearance which exceeds a predetermined value is forcibly reduced to a predetermined value.
It is frequently the case with sheet-processing printing machines that the at least one processing station of the latter, a feeder, which charges or feeds the processing station with the sheets, and the sheet conveyor of a delivery, the sheet conveyor transporting the sheets to the pile station, are in operative connection with one and the same drive, namely the main drive of the printing machine. A printing machine that is constructed in this manner and is equipped for implementing the method according to the invention thus cannot be operated if the vertical extent of the clearance beneath the sheet conveyor exceeds a predetermined value.
A preferred value of an acceptable vertical extent for startup of the printing machine is, in particular, in the order of magnitude of the dropping distance described hereinabove. If, for example, the lifting platform has not yet been charged with a pile and lowered completely, and an operator is doing, for example, preparatory work in the clearance space that is available, then the printing machine cannot be operated, with the result that the operator is not at any risk from the sheet conveyor, which includes gripper systems usually revolving during operation, gripping a respective processed sheet at the leading border thereof and, clamped in this manner, transporting the sheet to the pile station or, with the sheet run at a standstill, revolving in empty condition.
It is possible to start up the printing machine again only when the clearance space beneath the sheet conveyor has had the vertical extent thereof reduced to a predetermined acceptable magnitude. In the case assumed here of the lifting platform not yet having been charged with a pile and lowered completely, it is possible, for example, for the lifting platform to be raised, for the reduction of the clearance space, by corresponding manual activation of the aforementioned lifting-mechanism actuating motor so that the upper side of a pile base or board deposited on the lifting platform assumes the aforedescribed production level if preferably the sheet-dropping distance provided for the production printing constitutes a predetermined acceptable magnitude of the vertical extent of the clearance space.
A vertical extent of the clearance space which has been predetermined as acceptable in this way has indeed proven advantageous for the process control of the printing machine because, upon a startup of the latter, the sheet-dropping distance provided for the formation of a pile is already present; however, as regards safety, i.e., the screening of the sheet conveyor at such a height beneath the latter that an operator is not at any risk therefrom, larger vertical extents of the clearance space are also quite acceptable. At least any such extent wherein, depending upon the conception of a delivery including the sheet conveyor, access to the sheet conveyor is ruled out may be considered to be acceptable.
If, for example, when a given height of a pile formed from the processed sheets has been attained, the feeding of sheets to the printing machine is interrupted, the printing machine is switched into the xe2x80x9cprinting offxe2x80x9d operating condition or state thereof, the pile is removed from the pile station, with the lifting platform lowered completely for this purpose, and the lifting platform is provided with an empty pile base or board and raised to the production level again, then during this time, with the sheet conveyor coupled to the main drive of the printing machine, the gripper systems continue to revolve, but without transporting any sheets. In this case there is no risk of gripper systems at a standstill unexpectedly beginning to revolve, and immediate danger posed by the revolving gripper systems can clearly be seen so that it is probable that no operator will be directly exposed to this danger. However, in order to avoid any risks, one development preferably provides for forced stoppage of the drive following prior startup thereof if the extent of the clearance space exceeds a predetermined maximum acceptable value.
In the foregoing case, wherein a pile is transported away from the pile station, the clearance space is unacceptably exceeded at the latest when the pile which is to be removed has left the pile station, and the situation remains until an empty pile base or board has been raised to the production level.
In the described process, the interruption in the feeding of sheets to the printing machine takes place before the upper side of the pile, in particular by corresponding manual activation of the motor of the lifting mechanism, provided for lifting and lowering the lifting platform, with the lifting platform being lowered, reaches a level corresponding to an acceptable extent of the clearance space, and the lowering takes place after those sheets which are on the way to processing, after the interruption in the feeding of the sheets, are transferred to the pile.
In particular, due to the possibility of activating the motor of the lifting mechanism manually, it is also conceivable for an unacceptable extent of the clearance space to be present in an operating state of the printing machine wherein the fed sheets are being processed. Because stoppage of the drive in such an operating state of the printing machine would adversely affect the sheets located in the printing machine at the moment of stoppage of the drive, it is further preferably provided that following prior startup of the drive, with an extent of the clearance space beyond a predetermined value, it is only those sheets which were on the way to sheet processing which are still forcibly fed to the pile station, and then the drive is forcibly stopped.
This not only takes into account the aforementioned safety aspects, but also provides conditions under which spoilage or rejects are prevented from being produced.
One development also takes into account the safety aspects and the avoidance of rejects or spoilage to the effect that, as those sheets which were on the way to sheet processing are fed to the pile station, the extent of the clearance space cannot be increased in size.
As far as the pile-forming process is concerned, this development offers the advantage that a dropping distance, present once a predetermined extent of the clearance space has been exceeded, for the rest of the sheets which are to be stacked is not increased in size, with the result that, with the extent suitably predetermined, it is possible to avoid, in particular, a leading edge of a sheet coming into contact with the surface of a preceding, already deposited sheet, which otherwise, i.e., with an increased dropping distance, may occur in that a respective sheet, during contact of the sheet-braking system, still existing in a trailing region of the sheet, with the sheet in a leading region thereof, has been lowered considerably before it is deposited on the pile.
In the case of the afordescribed method of removing a pile from the pile station and subsequently forming a pile on an empty pile base or board, the clearance space located beneath the sheet conveyor extends in a vertical direction, depending upon the operating state of the printing machine, i.e., in particular of the delivery thereof, either to the upper side of the completely lowered lifting platform or to the upper side of a pile base or board deposited thereon or, during production printing, in particular to the upper side of a sheet respectively deposited at the production level for the purpose of forming a pile. A predetermined acceptable extent of the clearance space which is provided in this case approximately in the order of magnitude of the sheet-dropping distance, and includes the dropping distance, does indeed extend down at least to the production level, but an unacceptable extent of the clearance space is produced at the latest with the removal of the pile from the pile station, during which time the lifting platform is usually lowered completely. If this pile is, for example, the single or last pile of a printing job, then the lifting platform is usually left in the lowered position until a further printing job has been processed. In order, then, for the case of an operative connection of the sheet conveyor with the main drive, to be able to operate the latter with the empty lifting platform lowered in order to reset, in particular, the processing stations of the printing machine for a further printing job, for example, in order to change the printing plates in the case of an offset printing machine, a preferred development of the method of operating the printing machine provides that, by virtue of introducing into the clearance space a divider which can be moved into and removed from the clearance space, the vertical extent of the clearance space is limited to a predetermined acceptable value.
This means that, following prior stoppage of the main drive, which in the example at hand is operatively connected to the sheet conveyor, the blocking of that main drive is eliminated again, i.e., the previously stopped sheet conveyor can be operated again without the gripper systems thereof, which revolve during operation, posing any risk.
For this manner of operating a printing machine, for example, a suitable divider is a roller blind which, with the aforedescribed manner of removing a pile from the pile station and replacing it with an empty pile base or board, can be pushed into the clearance space, along stationary guides, so that, while limiting the clearance space to an acceptable extent, in a pushed-in position of the roller blind, the latter screens the sheet conveyor to prevent access.
A maximum acceptable extent of the clearance space, the stopped drive being blocked, and/or the operating drive being stopped if the extent is exceeded, is dimensioned, for a further type of pile which has been removed from the pile station being replaced by an empty pile base, in particular so that, with the divider moved into the clearance space, the clearance space has an extent that is smaller than the maximum acceptable extent.
This further type of pile which has been removed from the pile station being replaced by an empty pile base makes it possible not to interrupt the sheet processing during this operation. A delivery that is suitable for this purpose, a so-called non-stop delivery, has, in particular, a second lifting mechanism, a so-called auxiliary lifting mechanism, which is constructed for receiving a further pile base, a so-called auxiliary pile base, so that the latter, following prior lowering of an already built-up pile, referred to in this context as the main pile, a given distance in the clearance space, can be transferred to the auxiliary lifting mechanism. The auxiliary pile base transferred to the auxiliary lifting mechanism then collects sheets otherwise dropping onto the main pile and, for this purpose, is located, after the transfer thereof to the auxiliary lifting mechanism, first of all at such a level that the first sheets collected following the transfer are received thereby essentially at the production level described hereinbefore. As this process continues, the auxiliary lifting mechanism lowers the auxiliary pile base in a stepwise manner to the same extent as the height of a pile which is referred to in this context as an auxiliary pile increases, and builds up on the auxiliary pile base.
As soon as the auxiliary pile base has been transferred to the auxiliary lifting mechanism, the main pile is removed from the pile station, and the lifting platform, which has been freed of a full pile, is provided with an empty pile base and raised to such a level that, with the removal of the auxiliary pile base from the auxiliary lifting mechanism, the auxiliary pile built up in the interim on the auxiliary pile base can be transferred to the empty pile base then located on the lifting platform.
With the further aforedescribed type of pile which has been removed from the pile station being replaced by an empty pile base, the so-called non-stop delivery, the lowering of the main pile prior to the transfer of the auxiliary pile base to the auxiliary lifting mechanism increases the vertical extent of the clearance space by the specific distance mentioned. In this case, the lowering distance is only of such a magnitude as to allow the auxiliary pile base to collect the sheets essentially at the production level formed previously by the upper side of the main pile. The extent of the clearance space following this lowering operation, and prior to the transfer of the auxiliary pile base to the auxiliary lifting mechanism, thus has a still acceptable value, with the result that this lowering operation does not require the drive which is operatively connected to the sheet conveyor to be stopped. The auxiliary pile base, which is moved over the main pile following this lowering operation, thus reduces the vertical extent of the clearance space, with the result that an acceptable value for this extent is given once again and the drive, following prior startup thereof, rather than being forcibly stopped because an acceptable value for this extent has been exceeded, thus remains in operation without an operator being in any danger.
The auxiliary pile base thereby assumes the function of the divider.
In a preferred configuration of the method, extents of the clearance space which exceed predetermined values are detected, and an extent of the clearance space which exceeds a predetermined value is forcibly reduced to a predetermined value.
This can be dispensed with in the presence of the previously described, so-called non-stop delivery wherein, in particular, the auxiliary pile carrier is positioned manually in the clearance space, because it is possible for a pile to be changed in such a delivery without any adverse effects upon the formation of a pile of sheets of satisfactory quality only when the pile which is to be replaced by an empty pile base is lowered a relatively low value until the auxiliary pile base is positioned in the clearance space, so that the resulting increased extent of the clearance space still assumes a smaller value than a maximum acceptable extent allowed from the standpoint of safety.
If no non-stop delivery is present, however, the forced introduction of the divider into the clearance space, with an extent of the clearance space that exceeds a predetermined value, offers the advantage that the sheet conveyor, driven, if necessary or desirable, via the main drive of the printing machine, and thus the printing machine as a whole are not stopped if a complete pile is removed from the pile station. Instead, with the feeding of sheets interrupted and the printing machine shifted into the xe2x80x9cprinting offxe2x80x9d operating state, the divider forcibly introduced into the clearance space screens the gripper systems which, in this regard, revolve in an empty state.
All the acceptable vertical extents of the clearance space beneath the sheet conveyor which have been specified thus far, including a maximum acceptable extent which depends, respectively, upon the construction of the printing machine, have predeterminable values, these values being predetermined by the corresponding positioning of suitable detectors. The drive is stopped and/or kept at a standstill, in the different modes of the method described thus far, whenever the extent of the clearance space exceeds a maximum acceptable value.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as a method of operating a sheet-processing machine, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, wherein: